Step by step
The question
Question: draw a histogram of 5, 12, 18, 9, 14, 21, 11, 16, 13 and 7, in classes of 5.
How many are less than 15?
1 Make the classes
The smallest number is 5 and the biggest is 21.
In classes of 5: 5 to 9, 10 to 14, 15 to 19 and 20 to 24.
2 Make a frequency table
A frequency table first: one row for each class.
5 is in 5 to 9: a mark there, and we cross out 5.
12 is in 10 to 14.
And so on for every number.
We count the marks: 3, 4, 2 and 1.
3 Draw the bars
Along the bottom: the numbers, from 5 to 25.
Up the side: how many.
5 to 9: 3 numbers.
The bar covers 5 to 10 and goes up to 3.
10 to 14: 4.
15 to 19: 2.
Careful!
The bars touch.
The numbers go on with no gaps, like a number line.
A bar chart has gaps; a histogram does not.
4 Read the histogram
5 to 9: 3.
10 to 14: 4.
We add those bars: 3 plus 4 is 7.
5 Check
Let's check: all the bars together are 3 plus 4 plus 2 plus 1, which is 10.
That is every number in the list.
So it is right!
Let's look back.
First: make the classes.
Then: make a frequency table.
Then: draw the bars.
Then: read the histogram.
Last: check.